Electrically prepared subbing for photo-stencil film on polyethylene terephthalate support



United States Patent p 3,220,842 ELECTRICALLY PREPARED SUBBING FORPHOTO-STENCIL FILM 0N POLYETHYLENE TEREPHTHALATE SUPPORT John F.Carroll, Jr., and Robert D. Chapman, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey No Drawing. Filed Sept. 1, 1961, Ser. No. 135,431 4Claims. (Cl. 9683) This invention concerns polyethylene terephthalatesupport which has been electron bombarded for use with stripping films.

For many purposes, it is desirable to have a photographic strippingmaterial of the type in which the emulsion layer is carried by atemporary support and transferred from it subsequently. The types ofstripping films which are particularly useful in this connection arethose used for gravure resists and photo-stencil films. These films musthave sufficient emulsion-to-base adhesion to resist the strains ofemulsion drying after coating, and to withstand processing and drying.However, the emulsion must strip from the base as a unit without muchdifficulty for use as a resist or stencil.

Stripping films have been prepared on various temporary supports such ascellulose esters, paper, and the like. The photographic emulsion hasoften been coated onto some type of subcoating which was selectivelysoluble. For instance, a typical such soluble layer might be a celluloseacetate phthalate which would be soluble in the alkaline developersolution. Such a coating becomes strippable in the developer solution sothat it cannot be retained on the support satisfactorily in everyinstance unless care is taken in handling the photographic elementduring processing.

It has been desirable in the graphic arts field to employ film basematerial which has a high degree of dimensional stability. Supports ofthis type include polystyrene, polyesters, and the like. Polyethyleneterephthalate, in particular, has been suggested as a suitabledimensionally stable film support. However, this material is noted forbeing hydrophobic, and special treatments are necessary in order toobtain adhesion to the support.

Adhesion to polyethylene terephthalate can be obtained by flame treatingas described in US. Patent 3,072,- 483, issued January 8, 1963, in thenames of Trevoy and Phillips. Electron bombardment may be employed toobtain a hydrophilic surface. However, these treatments are used toobtain permanent adhesion of various materials to the surface ofpolyethylene terephthalate.

One object of this invention is to provide an electron bombardedpolyethylene terephthalate film support having a photoresist film. Anadditional object is to provide a method of preparing a thin basephoto-resist film employing polyethylene terephthalate as the filmsupport.

The above objects may be obtained by electron bombarding a polyethyleneterephthalate film base by passing it between two plates that areconnected to the pulsating D.C. output of a high voltage induction coil.In our preferred embodiment, a sheet of glass is used over one electrodeto prevent arcing, and the sheet of polyester passed over this glassplate between the two electrodes. This'leaves a gap of about 0.1"between the traveling film base and the exposed electrode. A coronadischarge takes place in this space and treats the side of thepolyethylene terephthalate support facing it. The support is then coatedon the treated side with the photographic emulsion or with a subcoatingover which is then coated a photographic emulsion.

The corona discharge must be produced from a source having an AC.component. However, it is not absolutely essential that a D.C. componentbe involved. Never- 3,220,842 Patented Nov. 30, 1965 theless, where aD.C. component is included, the direction of polarity may have an effecton the emulsion adhesion. The treatment is more effective if theelectrode facing the surface to be treated is negative. It will beappreciated that the conditions can be varied substantially with respectto the frequency, voltage output, electrode shape and conformation, typeand thickness of insulating sheet, electrode spacing, duration oftreatment, and polarity of any existing D.C. component.

Polyethylene terephthalate must be treated to a degree of adhesion whichprovides good adhesion to a photographic emulsion so that it will beretained on the support during photographic processing but will permitstripping of the film after the film has been processed and dried. Thistreatment on polyethylene terephthalate is peculiar in that while itproduces a tight bond which strongly resists accidental stripping, it isvery susceptible to peeling off of the emulsion once a corner is startedby means of a sharp edge.

The degree of wetability can be determined by the bubble method. Asample of the film is placed inside a water cell and a bubble holdercomprising a glass rod having a concave depression in the end of the rodmounted in a suitable movable support a short distance from the sampleso that a bubble of air can be placed between the bubble holder and thesample contacting both. The bubble holder should be mounted so that itcan be moved smoothly in a vertical direction to provide for eithercompressing or stretching the bubble while it remains in contact withthe sample. A suitable bubble is then placed under the bubble holder andthe bubble holder moved in the direction of the sample to compress thebubble, permitting it to extend sidewise beyond the edges of the bubbleholder. A line is taken tangent to the edge of the bubble where itcontacts the sample and the angle between this line and the surface ofthe sample measured. This is known as the receding contact angle.

In untreated polyethylene terephthalate the receding contact angle isabout 58, but in polyethylene terephthalate having a very high degree ofwetability, the angle can be 5 or less. A contact angle of less than 45indicates the correct amount of electron bombardment to provide anoperative substrate for use with a strippable coating such as aphotographic emulsion to provide a satisfactory stripping film.

Another method of determining the hydrophilic nature of the surface canbe employed involving measuring the contact angle of a drop of water onthe surface. A drop of distilled water is placed on a level sample. Byprojecting the image of the drop and sample on a suitable screen andmeasuring the angle obtained by drawing a line tangent to the drop imageat the point the edge of the drop touches the sample, this contact anglecan be measured quickly and accurately by using a Contour Projector asthe means of projection. Untreated polyethylene terephthalate film basegives a contact angle of about The minimum electron bombardment neededfor emulsion adhesion gives a contact angle of about 73f. Using the dropmethod, an angle of less than 73 would also be operative in adhering thecoatings such as the photographic emulsions to the support forstripping.

The photographic emulsion layer coated over the treated polyethyleneterephthalate support may be of any type, but for the copying ofdrawings, the emulsion is a high-contrast type. It is preferablyunhardened, since such an emulsion adheres much more strongly to asupport to which it may be transferred.

For use as a stencil, the emulsion also may contain a matting materialsuch as starch grains, diatomaceous earth, ground glass, barium sulfateor the like, which adds a tooth to the emulsion layer so that afterexposure and development, it can take pencil lines; thus permittingadditions to be made through the drawings.

In order to permit strong electron bombardment and yet achieve goodstripping when desired, the product is washed after processing bycontacting with 1-15 solution of stannous chloride, sodium stannite orother similar reducing agents for a long enough period for the solutionto penetrate the emulsion sufiiciently. This would normally be about oneto five minutes, but might be longer. This helps to loosen the preparedbond.

The following examples are intended to illustrate our invention but notto limit it in any way:

Example 1 A length of oriented polyethylene terephthalate film base towhich no surface layers had been applied was treated by passing itthrough two electrodes that were connected to the pulsating DC. outputof a high voltage induction coil. A sheet of glass was placed over oneelectrode, and a length of film rested on this glass plate as it passedbetween the plates. This left a gap of about 0.1" between the travelingsupport and the other electrode. The corona discharge took place in thisspace and treated the side of the support facing it. The recedingcontact angle was less than 45, measured using the bubble method. Thesupport was then coated with a gravure resist emulsion. No subbing layerwas used. This film was not susceptible to accidential damage eitherwhen dry or when wet. However, after it had been processed and dried,its dry stripping case was quite satisfactory.

Example 2 A length of organic polyethylene terephthalate film wastreated as in Example 1, but the support was coated in the sameoperation with a thin cellulose nitrate film having a thickness of .3mil from a solvent solution of cellulose nitrate in acetone. It was thensubbed using a gelatino aqueous solution and coated with a high-contrastunhardened photographic silver halide emulsion. After processing, thedry stripping ease was quite satisfactory.

Example 3 Organic polyethylene terephthalate as described in Example 1was washed following processing with water, in which sodium stannite wasadded to form a solution. The ease of stripping was improved over thatobtained in Example 1.

Example 4 A 5% solution of stannous chloride was used instead of sodiumstannite as in Example 3, with almost the same improvement in strippingover that obtained in Example 1.

It was found that when a photo-stencil image was formed that there wereusually areas where the dots were very small and formed isolated islandsof gelatin rather than a continuous skin. These areas have beenrecognized as very diflicult to strip. This is in direct contrast withthe normal kind of adhesion wherein the ease of stripping is increasedby dividing up the gelatin continuum into separate and discreet islands.However, the use of these added agents in the wash water resulted instripping these areas when the photo-stencil type emulsions wereemployed.

Various subs which may be used for coating the polyethyleneterephthalate film subsequent to the electron bombardment are those wellknown in the art. These include cellulose esters, such as cellulosenitrate, cellulose acetate, and the like; as well as other cellulosederivatives, such as cellulose ethers. Since some of the subs which areknown in the art become soluble in developers or in aqueous solutions,these subs will affect the adhesion of the emulsion coating which isplaced over the sub.

The degree and nature of stripping is the same beforeprocessing of theraw film as it is subsequent to processing, except when a special agent,such as a stannous derivative, is used as described above in the washwater. Although the examples show the use of the glass plate as asupport for the polyethylene terephthalate when it is passed between theelectrodes, it will be clear that other insulating materials may beused, such as several layers of polyethylene terephthalate,polytetrafiuoroethylene, and the like.

Our method of treating the polyethylene terephthalate support may beemployed for use for other stripping films. For instance, this speciallytreated support may be coated with separable sensitive layers which canbe transferred to suitable supports and capable of use in the imbibitionprocess of motion picture color photography.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. The method of facilitating the stripping of a gelatin silver halideemulsion from the electron bombarded surface of a polyethyleneterephthalate support which comprises contacting the support with thesilver halide emulsion thereon with a dilute aqueous solution containinga tin salt.

2. The method of facilitating the stripping of a gelatin silver halideemulsion layer from the electron bombarded surface of a polyethyleneterephthalate support which comprises contacting the support with theemulsion coating thereon with an aqueous solution containing 1-15 of acompound selected from a group consisting of the alkali metal stannitesalts and the stannous halide salts.

3. The method of facilitating the stripping of a gelatin silver halideemulsion from the electron bombarded surface of a polyethyleneterephthalate support which comprises washing the support with theemulsion thereon in about a 5% aqueous solution of sodium stannite.

4..The method of facilitating the stripping of a gelatin silver halideemulsion from the electron bombarded surface of a polyethyleneterephthalate support which comprises washing the support with theemulsion thereon in about a 5% aqueous solution of stannous chloride.

References Cited by the Examiner UNITED STATES PATENTS 3,035,915 5/1962Cohen etal 96-83 3,037,862 6/1962 Neth 9687 X 3,043,695 7/1962 AlleS96-83 3,072,483 1/1963 Trevoy of al 96-87 FOREIGN PATENTS 788,365 1/1958Great Britain.

1,159,702 2/1958 France.

OTHER REFERENCES Bopp et al.: Radiation Stability of Plastics andElastomers, US. Atomic Energy Commission, ORNL-1373, July 23, 1953, OakRidge National Laboratory, Oak Ridge, Tenn, pp. 1, 32, 33 and 64.

NORMAN G. TORCHIN, Primary Examiner.

1. THE METHOD OF FACILITATING THE STRIPPING OF A GELATIN SILVER HALIDEEMULSION FROM THE ELECTRON BOMBARDED SURFACE OF A POLYETHYLENETEREPHTHALATE SUPPORT WHICH COMPRISES CONTACTING THE SUPPORT WITH THESILVER HALIDE EMULSION THEREON WITH A DILUTE AQUEOUS SOLUTION CONTAININGA TIN SALT.